1. Field of the Invention
The present invention relates to a ferromagnetic tunnel junction element to sense a magnetic field and relates also to a device provided therewith such as tunnel magnetoresistive head, magnetic head slider, and magnetic disk drive.
2. Description of the Related Art
High-density magnetic recording needs a sophisticated read head. This requirement is met by the magnetoresistive head based on giant magnetoresistance effect (GMR effect), which has recently gained commercial acceptance. The current magnetoresistive head produces its GMR effect through the spin valve film composed of ferromagnetic layer, non-magnetic metal layer, and ferromagnetic layer. The spin valve film of this structure has a limited magnetoresistance ratio of about 10%. Hence, a more sensitive magnetoresistive element is required.
Researches to meet this requirement have recently revealed a phenomenon called ferromagnetic tunnel effect. This tunnel effect manifests itself in the junction structure composed of ferromagnetic layer, amorphous insulating layer, and ferromagnetic layer, and it depends on the relative angle of magnetization of the two ferromagnetic layers. (J. Magn. Mater. 139, L231 (1995); Phys. Rev. Lett. 74, 3273 (1995)) Because of its ability to give a magnetoresistance ratio greater than 10% at room temperature, the above-mentioned phenomenon has attracted keen attention on research and development for new magnetoresistive elements. For its extremely high sensitivity to magnetic field, the ferromagnetic tunnel effect film is greatly expected to find use as a read head for ultra-high-density magnetic recording exceeding 100 Gbit/inch2.
The ferromagnetic tunnel effect had been analyzed by Julliere""s theory (Phys. Lett. A54, 252 (1975)), which is useful particularly for the system containing an amorphous insulating layer. This theory defines the spin polarization as P=(D↑xe2x88x92D↓)/(D↑+D↓), where D↑ and D↓ denote respectively the density of state (or the number of states per unit energy) of up-spin and down-spin in the ferromagnetic layer at Fermi level. The value of P is used to represent the magnetoresistance ratio at zero voltage as follows.
xe2x80x83TMR=100xc3x972P2/(1xe2x88x92P2) [%]
The foregoing expression indicates that the larger the value of P, the higher the magnetoresistance ratio. This idea has stimulated the research on the tunnel junction with La0.7Sr0.3MnO3 which is a half-metallic ferromagnetic substance having P=1 at the absolute zero (Phys. Rev. Lett.,82,4288(1999)) This half-metallic ferromagnetic substance is regarded as an effective spin injector in view of the fact that only up-spin electrons contribute to conduction. This substance is under the stage of basic research and its practical application is being pursued.
The current tunnel magnetoresistive element represented by Co/Alxe2x80x94O/Co involves several problems in its practical use. The most serious among them is that the magnetoresistivity steeply decreases with increasing voltage. In other words, at the element""s operating voltage of 0.2-0.4V, the magnetoresistivity decreases by more than half from that at zero voltage. Moreover, Julliere""s expression suggests that the Co/Alxe2x80x94O/Co having an amorphous insulating layer would hardly give a magnetoresistivity higher than 40%.
On the other hand, it has been found that La0.7Sr0.3MnO3 as a spin injector does not work at room temperature because the terminal layer most contributive to conduction has a Curie temperature as low as about 180 K. Another problem is difficulty in film formation. Under these circumstance, it is an urgent issue to develop a new material or a new film construction.
Accordingly, it is an object of the present invention to provide a ferromagnetic tunnel junction element with film structure exhibiting high magnetoresistivity at finite voltage (including the element operating temperature) and devices provided therewith such as tunnel magnetoresistive head, magnetic head slider, and magnetic disk drive.
The present invention is directed to a ferromagnetic tunnel junction element of the type having a tunnel insulating layer and a first and second ferromagnetic layers arranged on both sides of said tunnel insulating layer, wherein said tunnel insulating layer is in indirect contact with said first and second ferromagnetic layers with a noble metal layer interposed between them.
The ferromagnetic tunnel junction element mentioned above has said noble metal layer in the form of single crystal of noble metal atoms or in the form of monoatomic layer or diatomic layer of noble metal atoms.
The ferromagnetic tunnel junction element mentioned above has said noble metal layer which contains any element of Au, Ag, and Cu.
The present invention is directed also to a magnetic disk drive of the type having a magnetic recording medium, a spindle motor to rotate said magnetic recording medium, a magnetic head which is so mounted on a slider as to perform information recording and reproducing on said magnetic recording medium, and an actuator to move said magnetic head to a desired position on the magnetic recording disk, wherein said magnetic head is provided with a ferromagnetic tunnel junction element and a power source to supply electric current thereto, said ferromagnetic tunnel junction element having a tunnel insulating layer and a first and second ferromagnetic layers arranged on both sides thereof, said tunnel insulating layer being in indirect contact with said first and second ferromagnetic layers with a noble metal layer interposed between them.
It is another object of the present invention to provide a magnetic disk drive of the type having a magnetic recording medium, a spindle motor to rotate said magnetic recording medium, a magnetic head which is so mounted on a slider as to perform information recording and reproducing on said magnetic recording medium, and an actuator to move said magnetic head to a desired position on the magnetic recording disk, wherein said magnetic head is provided with a ferromagnetic tunnel junction element and a power source to supply electric current thereto, said ferromagnetic tunnel junction element having a tunnel insulating layer and a first and second ferromagnetic layers arranged on both sides thereof, said tunnel insulating layer being in indirect contact with said first and second ferromagnetic layers with a noble metal layer interposed between them.
In the aforesaid magnetic disk drive, said first and second ferromagnetic layers contain Co or CoxFe1-x (x=0.7-1.0), and the aforesaid magnetic disk drive has a means to control the drive voltage applied to said ferromagnetic tunnel junction element above 0.01 V and below 0.1 V.
In the aforesaid magnetic disk drive, said first and second ferromagnetic layers contain Co or CoxFe1-x (x=0.7-1.0), and the aforesaid magnetic disk drive has a means to control the drive voltage applied to said ferromagnetic tunnel junction element above 0.2 V and below 0.5 V.
In the aforesaid magnetic disk drive, said first and second ferromagnetic layers contain Fe, and the aforesaid magnetic disk drive has a means to control the drive voltage applied to said ferromagnetic tunnel junction element above 0.01 V and below 0.15 V.
In the aforesaid magnetic disk drive, said first and second ferromagnetic layers contain Fe, and the aforesaid magnetic disk drive has a means to control the drive voltage applied to said ferromagnetic tunnel junction element above 0.3 V and below 0.7 V.
In the aforesaid magnetic disk drive, said first and second ferromagnetic layers contain NixFe1-x (x=0.7-1.0) and the aforesaid magnetic disk drive has a means to control the drive voltage applied to said ferromagnetic tunnel junction element above 0.03 V and below 0.06 V.
Other and further objects, features and advantages of the invention will appear more fully from the following description.